In known conventional photographic cameras, a filmstrip is advanced in a frame-by-frame manner along a transport path from a film cartridge to an exposure gate where the film can be exposed. The filmstrip is then advanced from the exposure gate onto a take-up spool, which is oppositely situated across the exposure gate from the film cartridge. In other known cameras, the filmstrip is initially prewound onto the take-up spool prior to exposing the film at the exposure gate, where it is eventually advanced into the film cartridge. In either of the above cameras, the filmstrip has a developed curvature occurring from the disposition of the filmstrip onto the spool of the cartridge or of the take-up spool. This curvature is alleviated sufficiently by means of a pressure plate which allows the filmstrip to lie flat when the filmstrip is presented at the exposure gate. A problem, however, which is common to both types of known cameras described above is the tendency of an unexposed portion of the filmstrip to develop a reverse set, or curl, which is opposite in nature from the type of curl common to filmstrips used in photographic cameras. This reverse curling typically develops in a transition area which is situated along the film transport path between the film cartridge chamber of the camera and the exposure gate (or, in the case of prewound cameras between the take-up spool chamber and the exposure gate). This reverse form of curling generally occurs after a period of camera inactivity in which the unexposed section of the filmstrip remains in the transition area. In addition to the amount of time the unexposed section of the filmstrip remains in the described transition area, environmental conditions, such as temperature and humidity, also affect the onset of a reverse curl. The end result is that the unexposed section of the filmstrip will not lie sufficiently flat despite the use of conventional pressure plates when the filmstrip is finally advanced by the camera into the exposure gate, creating a defocused image on the film and consequently, a blurred image on a processed print.
U.S. Pat. No. 4,720,721 describes a film advancing mechanism for a camera which moves a portion of unexposed film which has already developed a reverse form of curl beyond the exposure gate so that the curled film is not then exposed. As is apparent, this mechanism helps to avoid the taking of defocused pictures due to the onset of the reverse curling effect, but in the process a number of potential exposures (frames of film) can be wasted.
There is a need, therefore, to provide a camera having a film transport mechanism which minimizes the reverse curling effect on unexposed sections of a filmstrip by proactively preventing that occurrence.